The invention is directed to a method for rapid thermal processing of a semiconductor wafer by electromagnetic irradiation, comprising an irradiation arrangement for heating the semiconductor wafer preferably surrounded by a quartz chamber. This irradiation arrangement is composed of a plurality of light sources with the light of which the semiconductor wafer is irradiated at at least one side, as well as comprising a reflection chamber employed as a reflector that entirely encloses the semiconductor wafer and the light sources.
Such a method is disclosed, for example, by European Published Application 0 345 443, incorporated herein.
Rapid thermal processing methods (rapid thermal processing (RTP) or rapid thermal annealing (RTA)) are gaining greater and greater significance in the manufacture of electronic components on semiconductor wafers on a silicon or gallium arsenide basis. The principal advantages thereof--a reduced temperature stress and a rational manufacturing process--are utilized, among other things, in the manufacture of thin dielectrics, in silicidation reactions, and when flowing layers, for example of borphosphorous silicate glass. The semiconductor wafers are thereby individually introduced into a process chamber and are then very rapidly and optimally uniformly heated under a defined atmosphere by irradiation with an intense light source. A typical temperature-time cycle, for example, is a heating rate of 300.degree. C./sec to 1100.degree. C., a following annealing time of 5 sec at 1100.degree. C. and a cooling rate of 100.degree. C./sec.
An important condition for achieving high yields in rapid thermal processing is an adequately uniform temperature distribution over the semiconductor wafer. Particularly given large semiconductor wafer diameters, however, this demand represents a problem that has not yet been satisfactorily resolved. This shall be set forth below with reference to FIG. 1.
FIG. 1 schematically shows a widespread type of RTP system in section. The semiconductor wafer 1 to be heated is usually situated in a quartz chamber 2. The light source is composed of two rows of quartz halogen lamps (lamp banks 3). The reflector in the form of a cuboid reflection chamber 4 that surrounds the lamps and the semiconductor wafer 1 sees to it, on the one hand, that optimally low losses of the lamp light occur and also sees to it, on the other hand, that the losses due to thermal emission from the hot semiconductor wafer 1 are kept low. It is only possible to achieve high temperatures (&gt;1100.degree. C.) and a rapid heating in many RTP systems only when the area covered by the lamp banks is greater than the wafer area and the losses are kept minimal.
In FIG. 1, the light emitted by the lamps, and possibly singly or multiply reflected at the walls of the reflection chamber, is indicated by solid arrows, but with the heat emission being indicated by wavy arrows. It is known from the aforementioned, European Patent Application that the additional area at the semiconductor wafer edge 5 increases the heat emission thereat, this leading to a temperature that is reduced in comparison to the middle 6 of the semiconductor wafer. A uniform intensity distribution of the light, together with the non-uniform intensity distribution of the heat emission, therefore results in a temperature distribution that is non-uniform overall over the semiconductor wafer 1. A known possibility for correcting this is comprised in irradiating the semiconductor wafer edge 5 with increased intensity in comparison to the middle 6 of the semiconductor wafer, whereby the ratio of the intensities is constant during the entire annealing process. Although a uniform temperature distribution occurs as a result in this method, the rated temperature is only achieved after a certain time that is dependent on the thermal mass of the semiconductor wafer 1 and on the amount of the rated temperature, and that amounts to approximately 5 to 10 sec for six inch wafers. Given short annealing times (5 sec), regions at the semiconductor wafer edge 5 can therefore experience a temperature stressing that averages up to 50.degree. C. higher than regions in the middle 6 of the semiconductor wafer.
The different temperature-time curves at the edge and in the middle of the semiconductor wafer ultimately have a negative influence on the yield, particularly given large wafers, in the production of electronic components on a silicon basis. It is therefore proposed in the prior art to compensate the additional heat emission in the edge region of the semiconductor wafer with an additional irradiation directed onto the edge region whose intensity, however, is chronologically variable and which is controlled on the basis of temperature measurement or on the basis of previously calculated curve values such that a temperature distribution that is uniform overall is set during the entire annealing process. Specifically, for example, an additional reflection screen having a hemispherically arced cross section is proposed as a means for additional irradiation, this being arranged around the semiconductor wafer edge such that the heat emission proceeding therefrom is again reflected back onto the semiconductor wafer edge in a self-regulating fashion. It is proposed in a further exemplary embodiment having a cuboid reflection chamber entirely surrounding the lamps that the spacing between reflector and semiconductor wafer can be varied for compensating the temperature differences over the semiconductor wafer. Due to the complex control and/or additional light sources, however, this known method is relatively involved and is also complicated to manipulate.
The temperature distribution over the semiconductor wafer is fundamentally defined by the distribution of the following, two radiant contributions:
1. Intensity distribution of the lamp light, including multiple reflections at the wafer and at the reflector; PA1 2. Intensity distribution of the heat emission of the wafer that may potentially be reflected back thereonto (equivalent to a reduction in the losses relative to the case without back-reflection).
The possibility was already indicated above of compensating non-uniform losses that are generally greater at the wafer edge than in the middle thereof by increasing the intensity of the lamp light at the edge of the wafer relative to the wafer middle. The lamp intensity, however, can only be set such that a compensation occurs only for a specific temperature-time cycle. It must therefore be specifically readapted for every cycle since the transient temperature distribution otherwise gains insignificance given shorter times or faster heating, or conversely, the stationary temperature distribution gains insignificance given longer times over slower heating. Among other things, the problem is that techniques are in fact known that, for example, improve the uniform distribution of the losses but that these techniques, on the other hand, simultaneously deteriorate the distribution of the lamp light.
Foregoing reflection of the heat emission of the wafer by employing what is referred to as a black chamber also does not lead to the goal. The losses become so high that extremely high-intensity lamps having increased space requirements--not least of all for the power supply as well--must be utilized. Since, moreover, irradiation at both sides is needed in order to avoid temperature gradients in the wafer material caused by structures, such apparatus become extremely large. All other solutions that have hitherto been proposed are also not without their disadvantageous aspects.